Synthesis, Redox and Spectroscopic Properties of Nindigo and a Variety of Nindigo Coordination Compounds

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Synthesis, Redox and Spectroscopic Properties of Nindigo and a Variety of

Nindigo Coordination Compounds

by Graeme Nawn

M.Phil., University of Bath, 2008 M.Chem., University of Bath, 2006

A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of

DOCTOR OF PHILOSOPHY In the Department of Chemistry

 Graeme Nawn, 2013 University of Victoria

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Supervisory Committee

Synthesis, Redox and Spectroscopic Properties of Nindigo and a Variety of

Nindigo Coordination Compounds

by Graeme Nawn

M.Phil., University of Bath, 2008 M.Chem., University of Bath, 2006

Supervisory Committee

Dr. Robin G. Hicks, (Department of Chemistry)

Supervisor

Dr. Thomas M. Fyles, (Department of Chemistry)

Departmental Member

Dr. Lisa Rosenberg, (Department of Chemistry)

Dr. Al Boraston, (Department of Biochemistry)

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Supervisory Committee

Dr. Robin G. Hicks, (Department of Chemistry)

Supervisor

Dr. Thomas M. Fyles, (Department of Chemistry)

Dr. Lisa Rosenberg, (Department of Chemistry)

Dr. Al Boraston, (Department of Biochemistry)

Outside Member

Abstract

Ligand design plays an important role in the development and control of new coordination compounds. A new ligand architecture, Nindigo, has previously been reported and this study represents an expansion of that research to gain better insights into the attributes of this multifunctional ligand family.

Mono- and bis-palladium chelates of Nindigo have been synthesized with resulting electrochemical measurements allowing for the reversible redox-active nature of the ligand set to be identified. The electronic absorption properties of these complexes were also studied. The presence of the palladium centre was found to drastically perturb the ligand centered π-π* transition resulting in significant red shifts in the absorption spectra with respect to free Nindigo.

The main group coordination chemistry of Nindigo was explored by generating mono- and bis-BF2 Nindigo chelates. The electrochemical and spectral properties of these compounds were investigated with both families displaying weak emission in the NIR region. The bis-BF2 chelates were found to be sensitive in nature and decompose to the mono-BF2 chelates. In addition, heteroleptic complexes of mono-BF2 Nindigo chelates with palladium were also synthesized. The redox chemistry as well as the electronic absorption characteristics of these compounds provides a conceptual bridge between the two homologues.

Homoleptic zinc and copper complexes of mono-BF2 Nindigo chelates have been synthesized. The zinc derivative serves as an “innocent” system where all redox and spectral properties are ligand

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iv centered and the oxidation states of both the metal and surrounding ligands can be assigned. The copper complexes exhibit more diverse chemistry with the redox and electronic absorption properties differing dramatically from the zinc system. A combination of EPR, XPS and computational analysis suggests the copper systems to be non-innocent in nature.

In addition to the bis-bidentate anionic Nindigo ligand system, the fully oxidized neutral analogue has also been synthesized. DehydroNindigo exhibits significantly different chemical behaviour from Nindigo. Bridged ruthenium dimers have been synthesized that are obtained as two isomers, cis and trans (with respect to the bridging ligand). Both isomers exhibit rich electrochemical behaviour. The mixed valence states of both species are found, electrochemically, to be extremely stable with respect to disproportionation.

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List of Tables

Table 2.1: Selected bond lengths for 2.1b ... 23

Table 2.2: Optimized order of reagent addition for a selection of Nindigo derivatives ... 25

Table 2.3: Selected bond lengths for 1.32h and typical equivalent bond lengths from the literature ... 27

Table 2.4: UV/vis/NIR data from a variety of Nindigo’s ... 30

Table 2.5: Selected bond lengths for 1.32b’ ... 34

Table 2.6: Selected bond lengths and angles for 2.2c ... 41

Table 2.7: Electrochemical data for 2.2c and 1.33a (a = pseudo reversible, b = irreversible, c = net two electron process) ... 43

Table 3.1: Selected bond lengths and angles for 3.3b... 58

Table 3.2: Electrochemical data for mono-BF2 Nindigo chelates 3.3a and 3.3c (a = irreversible) ... 60

Table 3.3: Nitrogen-nitrogen distances of the bound and unbound cavities of derivatives of 3.3 ... 64

Table 3.4: Electrochemical data for derivatives of 3.5 ... 67

Table 3.5: Absorption and emission data for 3.3 and 3.5 ... 70

Table 3.6: Selected bond lengths and angles for 3.6a ... 74

Table 3.7: Electronic spectroscopy data for the homologues N-ptolyl Nindigo derivatives ... 76

Table 3.8: Electrochemical data for various derivatives of 3.6 (a quasi reversible, b irreversible) ... 77

Table 4.1: Selected bond lengths and angles for 4.1 ... 93

Table 4.2: Redox potentials for 4.1 (a = two coalesced oxidations, b = irreversible) ... 95

Table 4.3: Selected bond lengths and angles for 4.2a ... 198

Table 4.4: Electrochemical data for 4.2a and 4.2c (a = irreversible, b = pseudo reversible) ... 100

Table 4.5: Selected binding energy data for 4.2a and 4.2c as well as some selected standards ... 101

Table 4.6: Binding energy data for [4.2]+ and [4.2c]- ... 107

Table 5.1: Selected bond lengths for 5.1a with equivalent bond lengths obtained from the solid state structure of 2-tbutyl-3-ptolylimino-3H-indole148 ... 116

Table 5.2: Selected bond lengths and angles for 5.2b-trans ... 123

Table 5.3: Selected bond lengths and angles for 5.2b-cis ... 124

Table 5.4: Electrochemical data for 5.2h-trans and 5.2h-cis (a estimated from anodic peak only) ... 126

Table A-1: Crystallographic parameters ... 150

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Table B-2: Bond lengths (Å) and angles (o) for 2.1c ... 159

Table B-4: Bond lengths (Å) and angles (o) for 2.2d ... 165

Table B-5: Bond lengths (Å) and angles (o) for 3.3a ... 168

Table B-6: Bond lengths (Å) and angles (o) for 3.3b ... 171

Table B-9: Bond lengths (Å) and angles (o) for 3.3e ... 182

Table B-10: Bond lengths (Å) and angles (o) for 3.3f ... 184

Table B-14: Bond lengths (Å) and angles (o) for 4.1 ... 198

Table B-18: Bond lengths (Å) and angles (o) for 5.2b-trans ... 210

Table B-19: Bond lengths (Å) and angles (o) for 5.2b-cis ... 215

Table B-20: Bond lengths (Å) and angles (o) for 5.2h-trans ... 220

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List of Schemes

Scheme 1.1: Formation of N-sulfonylimines using TiCl4 ... 14

Scheme 1.2: Converting the carbonyl groups of anthraquinone to imines using TiCl4 ... 14

Scheme 1.3: General conditions used for Nindigo synthesis ... 15

Scheme 1.4: General conditions used for the synthesis of bis-Pd(hfac) chelates of Nindigo ... 16

Scheme 2.1: Attempted Nindigo formation employing a variety of Lewis Acids ... 20

Scheme 2.2: Attempted Nindigo synthesis employing silylamines ... 20

Scheme 2.3: Reactions of indigo with anilines to yield indigo-monoimines ... 22

Scheme 2.4: Reaction conditions for Nindigo synthesis ... 24

Scheme 2.5: MonoPalladium chelates of Nindigo as a result of trans/cis isomerization ... 39

Scheme 3.1: Conditions used for the synthesis of 3.3 ... 54

Scheme 3.2: Conditions employed to promote 3.5 as the major product ... 61

Scheme 3.3: Synthesis of palladium chelates of 3.3 ... 71

Scheme 4.1: Conditions for the synthesis of 4.1 ... 91

Scheme 4.2: General reaction conditions for the formation of 4.2 ... 96

Scheme 4.3: Reversible chemical oxidation of 4.2c to generate the cationic complex [4.2c]+ ... 104

Scheme 4.4: Reversible chemical reduction of 4.2c to generate the anionic complex [4.2c]- ... 105

Scheme 5.1: Synthesis of dehydroindigo ... 112

Scheme 5.2: Synthesis of dehydroindigodiimine144,145 ... 113

Scheme 5.3: Synthesis of dehydroNindigo (5.1) ... 113

Scheme 5.4: General conditions employed in attempted synthesis of 5.2-trans ... 119

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List of Figures

Figure 1.1: The three oxidation states of benzoquinone type molecules (neutral quinine, monoanionic

semiquinonate, and the dianionic catecholate) ... 4

Figure 1.2: The active site of galactose oxidase (GalOA) ... 5

Figure 1.3: Ligand based redox chemistry facilitating reductive elimination (top) and cycloaddition (bottom) reactions ... 6

Figure 1.4: The fundamental “H-chromophore” of Indigo ... 9

Figure 1.5: UV/vis/NIR spectra of Indigo at varying concentrations (left) and varying temperature (right) (reprinted with permission from Molecules)61 along with a photo of a saturated solution of indigo in DCM ... 10

Figure 1.6: Resonance contributions to the Indigo excited state ... 10

Figure 1.7: Bulkier indigoid derivatives ... 11

Figure 1.8: Early Indigo based coordination complexes, Indigo[Pd(nBuP)3Cl] (left) and octahydroindigo[Pd(Cl)PEt3]2 (right) ... 12

Figure 1.9: Rhenium indigo cluster ... 12

Figure 1.10: Postulated reactive intermediates during reaction ... 14

Figure 1.11: Postulated redox side reaction that occurs when the base contains unhindered α-hydrogen atoms ... 15

Figure 1.12: UV/vis/NIR spectra of 1.32b (blue), 1.32f (green), 1.32h (orange), 1.32i (purple), 1.32j (red). Spectra obtained in DCM at a concentration of 1.25 x 10-5 M ... 16

Figure 1.13: UV/vis/NIR spectra for previously synthesized 1.33b (blue), 1.33f (green), 1.33i (purple), 1.33j (red). Spectra obtained in DCM at a concentration of 1.25 x 10-5 M. Photograph of 1.33b in DCM solution (right) (all photographed solutions are approximately 0.1 μg/mL in DCM unless otherwise stated) ... 17

Figure 1.14: Example cyclic voltammogram of 1.33a ... 17

Figure 2.1: 1H NMR spectrum of 2.1c (Sample run in CD2Cl2)... 21

Figure 2.2: X-ray crystal structure of 2.1c. Thermal ellipsoids at the 50% probability level with all hydrogen atoms, with exception of the indole type hydrogen atoms, removed for clarity ... 22

Figure 2.3: UV/vis/NIR spectra of 2.1c (green) and 2.1d (red) Spectra obtained in DCM at a concentration of 1.25 x 10-5 M. Photograph of 2.1d in DCM solution (right) ... 23

Figure 2.4: Vinylogous amide resonance in indigo ... 24

Figure 2.5: 1H NMR of 1.32c (Sample run in CD2Cl2) ... 25

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Figure 2.7: X-ray crystal structure of 1.32h. Thermal ellipsoids at the 50 % probability level and all

hydrogen atoms, with exception of the indole type hydrogen atoms, removed for clarity ... 27

Figure 2.8: Fundamental chromophore of Nindigo ... 28 Figure 2.9: A comparison of UV/vis/NIR spectra for 2.1c (green) and 1.32c (red). Spectra obtained in

DCM at a concentration of 1.25 x 10-5 M ... 29

Figure 2.10: UV/vis/NIR spectra of 1.32a (purple), 1.32d (green) and 1.32e (orange). Spectra obtained in

DCM at a concentration of 1.25 x 10-5 M. Photographs of solutions of 1.32a (left) and 1.32d (right) ... 30

Figure 2.11: Normalized UV/vis/NIR spectra of 1.32c DCM (dark blue), acetone (red), THF (orange),

toluene (light blue), ethyl acetate (green), acetonitrile (grey), hexane (purple). Spectra obtained at a concentration approximately 1.25 x 10-5 M ... 31

Figure 2.12: Cyclic voltammogram of 1.32b showing two irreversible oxidations and numerous reduction

processes (DCM solution, 0.1 mM Bu4NBF4 electrolyte and scan rate = 100 mVs-1) ... 31

Figure 2.13: 1H NMR spectrum of the different product isolated from an attempted synthesis of 1.32b. (Sample run in CD2Cl2) ... 32

Figure 2.14: X-ray crystal structure of 1.32b’. Thermal ellipsoids at the 50% probability level with all

peripheral and aromatic hydrogen atoms removed for clarity ... 33

Figure 2.15: X-ray crystal structure of a non-centrosymmetric para-fluorinated indigodiimine (generated

from deposited coordinates) with all peripheral and aromatic hydrogen atoms removed for clarity78 ... 35

Figure 2.16: Tautomerisation of indigo diimine ... 35 Figure 2.17: UV/vis/NIR spectra of 1.32b (blue) and 1.32b’ (green). Spectra obtained from DCM at a

concentration of 1.25 x 10-5 M. Photograph of a solution of 1.32b’ (right) ... 36

Figure 2.18: UV/vis/NIR spectra showing the conversion of 1.32b’ to 1.32b over 16 days in DCM (Red =

zero days, purple = four days, blue = 8 days, green = 16 days) ... 36

Figure 2.19: UV/vis/NIR spectra showing the persistence of 1.32b’ over 16 days in DMSO (blue = zero

days, red = 16 days) ... 37

Figure 2.20: 1H NMR and 19F NMR (inset) of the monopalladium chelate of 2.2c (sample run in CD2Cl2) 40

Figure 2.21: X-ray crystal structure of 2.2c. Thermal ellipsoids at the 50% probability level with all

hydrogen atoms, except for the acidic proton that is retained for charge balance, removed for

clarity ... 41

Figure 2.22: X-ray structures of 2.2c (left) and 1.33b (right) viewed across the central carbon-carbon

bond. All hydrogen atoms and hfac units removed for clarity ... 42

Figure 2.23: UV/vis/NIR spectra for 2.2c (purple) and 2.2d (red). Spectra obtained in DCM at a

concentration of 1.25 x 10-5 M. Photograph of 2.2c (right) ... 42

Figure 2.24: Cyclic voltammogram for 2.2c (bottom) and 1.33a (top) (DCM solution, 0.1 mM Bu4NBF4 electrolyte and scan rate = 100 mVs-1) ... 43

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Figure 3.1: Representative examples of NIR chromophores based on N-donor macrocycles109,110 ... 51

Figure 3.2: A variety of tuned BODIPY type structures ... 52

Figure 3.3: Various C3N3 based NIR absorbing systems with the β-diketiminate chelating environment highlighted in Nindigo (right)127,130,139 ... 53

Figure 3.4: The common C3N2 binding motif found in a variety of BODIPY derivatives highlighted for Nindigo in red ... 53

Figure 3.5: 1H NMR spectrum of 3.3d (Sample run in CD2Cl2) ... 55

Figure 3.6: 19F (left) and 11B (right) spectra of 3.3d (Samples run in CD2Cl2) ... 55

Figure 3.7: 19F (left) and 11B (right) NMR spectra for 3.3e (Samples run in CD2Cl2) ... 56

Figure 3.8: X-ray crystal structure of 3.3b. Thermal ellipsoids at the 50% probability level with all hydrogen atoms, with the exception of the indole type hydrogen, removed for clarity ... 57

Figure 3.9: X-ray crystal structures of 3.3d (left) and 3.3e (right) viewed down the central carbon-carbon bond. Thermal ellipsoids at the 50% probability level and all hydrogen atoms removed for clarity ... 58

Figure 3.10: UV/vis/NIR spectra for 3.3b (blue), 3.3d (green) and 3.3f (brown). Spectra obtained in DCM at a concentration of 1.25 x 10-5 M. Photograph of a solution of 3.3c (right) ... 59

Figure 3.11: Cyclic voltammograms of 3.3a (top) and 3.3c (bottom) (DCM solution, 0.1 mM Bu4NBF4 electrolyte and scan rate = 100 mVs-1) ... 60

Figure 3.12: 1H NMR spectrum of 3.5c (Sample run in CD2Cl2) ... 62

Figure 3.13: 19F (left) and 11B (right) NMR spectra of 3.5c (Samples run in CD2Cl2) ... 62

Figure 3.14: UV/vis/NIR spectra of 1.32b (red), 3.3b (blue) and 3.5b (green). Spectra obtained in DCM at a concentration of 1.25 x 10-5 M. Photograph of a solution of 3.5d (right) ... 63

Figure 3.15: Time dependant 19F NMR showing conversion of 3.5b to 3.3b in dry degassed CD2Cl2 at room temperature (left) and time dependent UV/vis/NIR spectroscopy showing the conversion of 3.5d to 3.3d in DCM over 90 hours ... 65

Figure 3.16: Cyclic voltammogram of 3.5a (purple), 3.5b (blue), 3.5c (red), 3.5d (green), 3.5f (brown) (DCM solution, 0.1 mM Bu4NBF4 electrolyte and scan rate = 100 mVs-1) ... 66

Figure 3.17: ortho-unsubstituted skeleton of 3.5 (left) and ortho-substituted skeleton of 3.5 (right) showing aryl twist hindering free rotation ... 67

Figure 3.18: Calculated bond lengths for 3.3a (left red) and experimental bond lengths for 3.3a (left blue). Calculated bond lengths for 3.5a (right) ... 68

Figure 3.19: FMO contour plots and energies for 3.3a and 3.5a ... 769

Figure 3.20: Emission spectra of selected derivatives of 3.4 (left, black = 3.4d, blue = 3.4e, green = 3.4a) and 3.5 (right blue = 3.5d, green = 3.5b). The sharp peaks are due to the laser source ... 70

Figure 3.21: 1H NMR spectrum of 3.6b (Sample run in CD2Cl2) ... 72

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Figure 3.23: X-ray crystal structure of 3.6a. Thermal ellipsoids at the 50% probability level and all

hydrogen atoms removed for clarity ... 73

Figure 3.24: X-ray crystal structures of 1.33b (left), 3.6a (centre) and 3.6d (right) showing core puckering

(all proton, hfac units and N-aryl substituents removed for clarity) ... 75

Figure 3.25: UV/vis/NIR spectra of 3.6a (purple), 3.6b (blue), 3.6c (red) and 3.6d (green). Spectra

obtained in DCM at a concentration of 1.25 x 10-5 M. Photograph of a solution of 3.6a (right) ... 75

Figure 3.26: UV/vis/NIR spectra of the complete pTol family. 1.32b (blue), 3.3b (red), 3.5b (green), 3.6b

(purple), 1.33b (orange). All spectra obtained from DCM at a concentration of 1.25 x 10-5 M ... 76

Figure 3.27: Cyclic voltammograms for 3.6a (purple), 3.6b (blue), 3.6c (red), 3.6d (green) and 3.6f

(brown) (DCM solution, 0.1 mM Bu4NBF4 electrolyte and scan rate = 100 or 250 mVs-1) ... 77

Figure 3.28: Cyclic voltammograms for 1.33a (top), 3.6a (blue) and 3.3a (red) (DCM solution, 0.1 mM

Bu4NBF4 electrolyte and scan rate = 100 mVs-1) ... 78

Figure 3.29: FMO contour plots and energies for 3.5a, 3.6a and 1.33a ... 79 Figure 4.1: A unique cycle involving both valence tautomerism and redox activity (left). An example of a

valence tautomeric complex involving copper and a multidentate redox-active N-heterocyclic ligand (right)139,140 ... 90

Figure 4.2: 11B (left) and 19F (right) NMR spectra for 4.1 (Samples run in CD2Cl2) ... 92

Figure 4.3: X-ray crystal structure of 4.1. Ellipsoids at the 50% probability level with all hydrogen atoms

removed for clarity ... 93

Figure 4.4: UV/vis/NIR spectra of 3.6a (red) and 4.1 (green). Samples run at 1.25 x 10-5 M in DCM. Photograph of a solution of 4.1 (right) ... 94

Figure 4.5: Cyclic voltammogram of 4.1 (DCM solution, 0.1 mM Bu4NBF4 electrolyte and scan rate = 100 mVs-1) ... 95

Figure 4.6: X-ray crystal structure of 4.2c. Ellipsoids at the 50% probability level with all hydrogen atoms

Figure 4.7: UV/vis/NIR spectrum of 4.2a. Sample run at 1.25 x 10-5 M in DCM. Photograph of a solution of 4.2a (right) ... 99

Figure 4.8: UV/vis/NIR spectrum of low energy transitions of 4.2a (* artifacts of spectrometer) ... 99 Figure 4.9: Cyclic voltammograms of 4.2c (top) and 4.2a (bottom) (DCM solution, 0.1 mM Bu4NBF4 electrolyte and scan rate = 100 mVs-1) ... 100

Figure 4.10: XPS data for 4.2a (purple, labelled Cu(MBPhen)2 in caption) and 4.2c (blue, labelled Cu(MBDmp)2 in caption) against a variety of Cu(I) and Cu(II) standards (all XPS experiments run by the group of T. Storr, Simon Fraser University) ... 101

Figure 4.11: Solid state (powder sample at room temperature) EPR spectrum of 4.2a ... 102 Figure 4.12: Spin density diagram for 4.2a ... 102

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Figure 4.13: Schematic representation of the possible electronic structures of 4.2a ... 103 Figure 4.14: UV/vis/NIR of 4.2c (green), [4.2c]+ (purple) and that obtained from the reduction of [4.2c]+ (red) (*artifact from the spectrometer)... 105

Figure 4.15: UV/vis/NIR spectra of 4.2c (green), [4.2c]- (purple) and that obtained by oxidation of [4.2c] -(red) ... 106

Figure 4.16: XPS data for 4.2c, [4.2c]+ and [4.2c]- ... 107

Figure 4.17: Low temperature [toluene (red), DCM (green)] and room temperature [toluene (blue), DCM

(purple)] UV/vis/NIR spectra for 4.2c ... 108

Figure 5.1: 1H NMR spectrum for 5.1c (Sample run in CD2Cl2) ... 114

Figure 5.2: Aromatic region of the 1H NMR spectrum for 5.1a. (Sample run in CD2Cl2) ... 115

Figure 5.3: Single crystal X-ray structure of 5.1a. Thermal ellipsoids set at the 50% probability level. All

hydrogen atoms removed for clarity ... 116

Figure 5.4: Structure of 2-tButyl-3-ptolyl-3H-indole ... 117 Figure 5.5: UV/vis/NIR spectrum of 5.1a. Sample run in DCM at a concentration of 1.25 x 10-5 M.

Photograph of a solution of 5.1a (right) ... 117

Figure 5.6: Cyclic voltammogram of 5.1a (DCM solution, 0.1 mM Bu4NBF4 electrolyte and scan rate = 240 mVs-1) ... 118

Figure 5.7: 1H NMR of fraction one (top) with 19F NMR (inset). 1H NMR of fraction two (bottom) with 19F NMR (inset). Samples run in CD2Cl2 ... 120

Figure 5.8: Single crystal X-ray structure of 5.2b-trans (left) all hydrogen, fluorine and hfac carbons

atoms removed for clarity. Alternate view of 5.2b-trans (right) with all hydrogen and hfac atoms

removed for clarity. Thermal ellipsoids set at the 50% probability level ... 122

Figure 5.9: Single crystal X-ray structure of 5.2b-cis (left) with all fluorine, hydrogen and hfac carbons

removed for clarity. Alternative view of 5.2b-cis (right) with all hydrogen and hfac atoms removed for clarity. Thermal ellipsoids set at the 50 % probability level ... 124

Figure 5.10: UV/vis/NIR spectra for 5.2h-trans (blue) and 5.2h-cis (red). Spectra obtained in DCM at a

concentration of 1.25 x 10-5 M. Photograph of a solution of 5.2h-trans (left) and 5.2h-cis (right) ... 125

Figure 5.11: Cyclic voltammograms of 5.2h-trans (top) and 5.2h-cis (bottom). (DCM solution, 0.1 mM

Bu4NBF4 electrolyte and scan rate = 100 mVs-1) ... 126

Figure 5.12: MO diagram showing no metal-metal communication (left) and metal-metal

communication facilitated by a bridge (right) ... 127

Figure 5.13: Equation showing comproportionation calculation (top) and schematic showing the redox

processes involved (bottom) ... 127

Figure 5.14: Electron transfer (top) and hole transfer (bottom) mechanism for valence exchange in a

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Figure 5.15: UV/vis/NIR spectra of [5.2h-trans]+ (red) and [5.2h-cis]+ (green) ... 130

Figure 5.16: UV/vis/NIR spectra of [5.2h-trans]- (red) and [5.2h-cis]- (green) ... 131

Figure B-1: ORTEP view of 1.32b’. Thermal ellipsoids at the 50% probability level with all hydrogen

atoms, with the exception of the N-H atoms, removed for clarity... 156

Figure B-2: ORTEP view of two crystallographically independent molecules of 2.1c, A (left) and B (right).

Thermal ellipsoids at the 50% probability level with all hydrogen atoms, with the exception of the N-H atoms, removed for clarity ... 158

Figure B-3: ORTEP view of 2.2c. Thermal ellipsoids at the 50% probability level with all hydrogen atoms,

with the exception of the imine bridged hydrogen atom, removed for clarity ... 161

Figure B-4: ORTEP view of 2.2d. Thermal ellipsoids at the 50% probability level with all hydrogen atoms,

with the exception of the N-H atoms, removed for clarity... 164

Figure B-5: ORTEP view of the two crystallographically independent molecules of 3.3a, A (left) and B

(right). Thermal ellipsoids at the 50% probability level with all hydrogen atoms, with the exception of the N-H atoms, removed for clarity ... 167

Figure B-6: ORTEP view of 3.3b. Thermal ellipsoids at the 50% probability level with all hydrogen atoms,

with the exception of the N-H atom, removed for clarity ... 170

Figure B-7: ORTEP view of the two crystallographically independent molecules of 3.3c, A (left) and B

Figure B-8: ORTEP view of the two crystallographically independent molecules of 3.3d, A (left) and B

Figure B-9: ORTEP view of 3.3e. Thermal ellipsoids at the 50% probability level with all hydrogen atoms,

with the exception of the N-H atom, removed for clarity ... 181

Figure B-10: ORTEP view of 3.3f. Thermal ellipsoids at the 50% probability level with all hydrogen

atoms, with the exception of the N-H atom, removed for clarity ... 183

Figure B-11: ORTEP view of 3.6a. Thermal ellipsoids at the 50% probability level with all hydrogen

atoms removed for clarity ... 186

Figure B-12: ORTEP view of the two crystallographically independent molecules of 3.6c, A (left) and B

(right). Thermal ellipsoids at the 50% probability level with all hydrogen atoms removed for clarity ... 189

Figure B-13: ORTEP view of 3.6d, A (left) and B (right). Thermal ellipsoids at the 50% probability level

with all hydrogen atoms removed for clarity ... 194

Figure B-14: ORTEP view of 4.1. Thermal ellipsoids at the 50% probability level with all hydrogen atoms

Figure B-15: ORTEP view of 4.2a. Thermal ellipsoids at the 50% probability level with all hydrogen atoms

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Figure B-16: ORTEP view of 4.2c. Thermal ellipsoids at the 50% probability level with all hydrogen atoms

Figure B-17: ORTEP view of 5.1a. Thermal ellipsoids at the 50% probability level with all hydrogen atoms

Figure B-18: ORTEP view of 5.2b-trans. Thermal ellipsoids at the 50% probability level with all hydrogen

atoms removed for clarity. 5.2b-trans presents as a racemate of ΛΛ and ΔΔ isomers ... 209

Figure B-19: ORTEP view of 5.2b-cis. Thermal ellipsoids at the 50% probability level with all hydrogen

atoms removed for clarity. 5.2b-cis present as a racemate of ΛΛ and ΔΔ isomers ... 214

Figure B-20: ORTEP view of 5.2h-trans. Thermal ellipsoids at the 50% probability level with all hydrogen

atoms removed for clarity. 5.2h-trans presents as a racemate of ΛΛ and ΔΔ isomers ... 219

Figure B-21: ORTEP view of 5.2b-cis. Thermal ellipsoids at the 50% probability level with all hydrogen

atoms removed for clarity. 5.2h-cis presents as a racemate of ΛΔ and ΔΛ isomers ... 223

Figure C-1: Cyclic voltammogram of 2.2d (CH2Cl2 solution, 0.1 mM Bu4NBF4 electrolyte and scan rate 100 mVs-1) ... 228

Figure C-2: Cyclic voltammogram of 3.3b (CH2Cl2 solution, 0.1 mM Bu4NBF4 electrolyte and scan rate 100 mVs-1) ... 228

Figure C-4: Cyclic voltammogram of 3.3e (CH2Cl2 solution, 0.1 mM Bu4NBF4 electrolyte and scan rate 100 mVs-1) ... 229

Figure C-5: Cyclic voltammogram of 3.3f (CH2Cl2 solution, 0.1 mM Bu4NBF4 electrolyte and scan rate 100 mVs-1) ... 229

Figure C-7: Cyclic voltammogram of 3.6c (CH2Cl2 solution, 0.1 mM Bu4NBF4 electrolyte and scan rate 100 mVs-1) ... 230

Figure C-9: Cyclic voltammogram of 5.1a (CH2Cl2 solution, 0.1 mM Bu4NBF4 electrolyte and scan rate 100 mVs-1) ... 230

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Figure C-11: Cyclic voltammogram of 5.1c (CH2Cl2 solution, 0.1 mM Bu4NBF4 electrolyte and scan rate

100 mVs-1) ... 231

Figure C-12: Cyclic voltammogram of 5.2b-trans (CH2Cl2 solution, 0.1 mM Bu4NBF4 electrolyte and scan rate 100 mVs-1) ... 231

Figure C-13: Cyclic voltammogram of 5.2b-cis (CH2Cl2 solution, 0.1 mM Bu4NBF4 electrolyte and scan rate rate 100 mVs-1) ... 232

Figure D-1: 1H NMR of 1.32a. Peaks at 5.32 ppm due to solvent and 1.53 ppm due to residual water (Expected elemental analysis C 81.53 %, H 4.89 %, N 13.58 %; experimental C 77.04 %, H 4.58 %, 12.87 %) ... 233

Figure D-2: 13C NMR of 1.32a ... 234

Figure D-3: 1H NMR of 1.32b. Peaks at 5.32 ppm due to solvent and 1.52 ppm due to residual water . 234 Figure D-4: 13C NMR of 1.32b ... 235

Figure D-5: 1H NMR of 1.32c. Peaks at 5.32 ppm due to solvent ... 235

Figure D-6: 13C NMR of 1.32c ... 236

Figure D-7: 1H NMR of 1.32d. Peaks at 5.32 ppm due to solvent and 1.52 ppm due to residual water . 236 Figure D-8: 13C NMR of 1.32d ... 237

Figure D-9: 1H NMR of 1.32e. Peaks at 5.32 ppm due to solvent and 1.52 ppm due to residual water . 237 Figure D-10: 13C NMR of 1.32e ... 238

Figure D-11: 1H NMR of 1.32g. Peaks at 5.32 ppm due to solvent and 1.52 ppm due to residual water 238 Figure D-12: 13C NMR of 1.32g ... 239

Figure D-13: 1H NMR of 1.32b’. Peaks at 5.32 ppm due to solvent and 1.52 ppm due to residual water239 Figure D-14: 13C NMR of 1.32b’ ... 240

Figure D-15: 1H NMR of 2.1c. Peaks at 5.32 ppm due to solvent and 1.54 ppm due to residual water .. 240

Figure D-16: 13C NMR of 2.1c ... 241

Figure D-19: 1H NMR of 2.2c. Peak at 5.32 ppm due to solvent ... 242

Figure D-20: 13C NMR of 2.2c ... 243

Figure D-21: 19F{1H} NMR of 2.2c ... 243

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Figure D-25: 1H NMR of 3.3a. Peaks at 5.32 ppm due to solvent and 1.54 ppm due to residual water . 245

Figure D-26: 13C NMR of 3.3a ... 246

Figure D-27: 19F{1H} NMR of 3.3a ... 246

Figure D-18: 11B NMR of 3.3a ... 247

Figure D-29: 1H NMR of 3.3b. Peaks at 5.32 ppm due to solvent and 1.57 ppm due to residual water . 247

Figure D-30: 13C NMR of 3.3b ... 248

Figure D-31: 19F{1H} NMR of 3.3b ... 248

Figure D-32: 11B NMR of 3.3b ... 249

Figure D-34: 13C NMR of 3.3c ... 250

Figure D-36: 11B NMR of 3.3c ... 251

Figure D-37: 1H NMR of 3.3d. Peaks at 5.32 ppm due to solvent and 1.52 ppm due to residual water . 251

Figure D-38: 13C NMR of 3.3d ... 252

Figure D-39: 19F{1H} NMR of 3.3d ... 252

Figure D-40: 11B NMR of 3.3d ... 253

Figure D-41: 1H NMR of 3.3e. Peaks at 5.32 ppm due to solvent and 1.52 ppm due to residual water . 253

Figure D-42: 13C NMR of 3.3e ... 254

Figure D-43: 19F{1H} NMR of 3.3e ... 254

Figure D-44: 11B NMR of 3.3e ... 255

Figure D-45: 1H NMR of 3.3f. Peaks at 5.32 ppm due to solvent and 1.52 ppm due to residual water .. 255

Figure D-46: 13C NMR of 3.3f ... 256

Figure D-47: 19F{1H} NMR of 3.3f ... 256

Figure D-48: 11B NMR of 3.3f ... 257

Figure D-49: 1H NMR of 3.5a. Peaks at 7.24 ppm due to solvent and 1.52 ppm due to residual water . 257

Figure D-51: 11B NMR of 3.5a ... 258

Figure D-52: 1H NMR of 3.5b. Peaks at 5.32 ppm due to solvent and 1.52 ppm due to residual water . 259

Figure D-53: 13C NMR of 3.5b ... 259

Figure D-55: 11B NMR of 3.5 ... 260

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xix

Figure D-57: 13C NMR of 3.5c ... 261

Figure D-59: 11B NMR of 3.5c ... 262

Figure D-63: 11B NMR of 3.5d ... 264

Figure D-64: 1H NMR of 3.5f. Peaks at 5.32 ppm due to solvent and 1.52 ppm due to residual water .. 265

Figure D-66: 11B NMR of 3.5f ... 266

Figure D-67: 1H NMR of 3.6a. Peaks at 7.24 ppm due to solvent and 1.52 ppm due to residual water . 266 Figure D-68: 13C NMR of 3.6a ... 267

Figure D-69: 19F{1H} NMR of 3.6a ... 267

Figure D-70: 11B NMR of 3.6a ... 268

Figure D-74: 11B NMR of 3.6b ... 270

Figure D-76: 13C NMR of 3.6c ... 271

Figure D-78: 11B NMR of 3.6c ... 272

Figure D-81: 19F{1H} NMR of 3.6d ... 273

Figure D-82: 11B NMR of 3.6d ... 274

Figure D-83: 1H NMR of 3.6f. Peaks at 5.32 ppm due to solvent, 1.97ppm due to MeCN and 1.52 ppm due to residual water ... 274

Figure D-84: 13C NMR of 3.6f ... 275

Figure D-86: 11B NMR of 3.6f ... 276

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xx

Figure D-88: 13C NMR of 4.1 ... 277

Figure D-89: 19F{1H} NMR of 4.1 ... 277

Figure D-90: 11B NMR of 4.1 ... 278

Figure D-91: 1H NMR paramagnetic of 4.2a. Peaks at 5.32 ppm due to solvent and 1.52 ppm due to residual water ... 278

Figure D-92: 1H NMR paramagnetic (zoom) of 4.2a. Peaks at 5.32 ppm due to solvent and 1.52 ppm due to residual water ... 279

Figure D-94: 1H NMR of 5.1a. Peaks at 5.32 ppm due to solvent and 1.52 ppm due to residual water . 280 Figure D-95: 13C NMR of 5.1a ... 280

Figure D-99: 13C NMR of 5.1c ... 282

Figure D-100: 1H NMR of 5.1h. Peaks at 5.32 ppm due to solvent and 1.53 ppm due to residual water 283 Figure D-101: 13C NMR of 5.1h ... 283

Figure D-102: 1H NMR of 5.2b-trans. Peaks at 5.32 ppm due to solvent and 1.52 ppm due to residual water ... 284

Figure D-103: 13C NMR of 5.2b-trans ... 284

Figure D-104: 19F{1H} NMR of 5.2b-trans ... 285

Figure D-105: 1H NMR of 5.2h-trans. Peaks at 5.32 ppm due to solvent and 1.53 ppm due to residual water ... 285

Figure D-106: 13C NMR of 5.2h-trans ... 286

Figure D-107: 19F{1H} NMR of 5.2h-trans ... 286

Figure D-108: 1H NMR of 5.2b-cis. Peaks at 5.32 ppm due to solvent and 1.52 ppm due to residual water ... 287

Figure D-109: 13C NMR of 5.2b-cis ... 287

Figure D-110: 19F{1H} NMR of 5.2b-cis ... 288

Figure D-111: 1H NMR of 5.2h-cis. Peaks at 5.32 ppm due to solvent and 1.52 ppm due to residual water ... 288

Figure D-112: 13C NMR of 5.2h-cis ... 289

Figure D-113: 19F{1H} NMR of 5.2h-cis ... 289

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xxi

Figure E-2: HRMS of 1.32b [theoretical (top), experimental (bottom)] ... 290

Figure E-3: HRMS of 1.32c [theoretical (bottom), experimental (top)] ... 291

Figure E-4: HRMS of 1.32d [theoretical (top), experimental (bottom)] ... 291

Figure E-1: HRMS of 1.32e [theoretical (top), experimental (bottom)] ... 292

Figure E-6: HRMS of 1.32g [theoretical (bottom), experimental (top)] ... 292

Figure E-7: HRMS of 2.1c [experimental] ... 293

Figure E-8: HRMS of 2.1d [experimental] ... 293

Figure E-9: HRMS of 3.3a [theoretical (top) experimental (bottom)] ... 294

Figure E-10: HRMS of 2.2c (experimental) ... 294

Figure E-11: HRMS of 2.2d (experimental) ... 295

Figure E-12: HRMS of 3.3b [theoretical (bottom) experimental (top)] ... 295

Figure E-13: HRMS of 3.3c [theoretical (top) experimental (bottom)] ... 296

Figure E-14: HRMS of 3.3d [theoretical (bottom) experimental (top)] ... 296

Figure E-15: HRMS of 3.3e [theoretical (bottom) experimental (top)] ... 297

Figure E-16: HRMS of 3.3f experimental ... 297

Figure E-17: HRMS of 3.5a [experimental] ... 298

Figure E-18: HRMS of 3.5b [experimental] ... 298

Figure E-22: HRMS of 3.6b [experimental] ... 300

Figure E-25: HRMS of 4.1 [experimental] ... 302

Figure E-28: HRMS of 5.1a [theoretical (top), experimental (bottom)] ... 303

Figure E-29: HRMS of 5.1b [theoretical (top and middle), experimental (bottom)] ... 304

Figure E-31: HRMS of 5.1h [experimental] ... 305

Figure E-32: HRMS of 5.2b-trans [experimental] ... 305

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xxii

Figure E-34: HRMS of 5.2b-cis [experimental (bottom), theoretical (middle)] ... 306 Figure E-35: HRMS of 5.2h-cis [experimental (top), theoretical (bottom)] ... 307 Figure F-1: UV/vis/NIR spectrum of 1.32b ... 307 Figure F-2: UV/vis/NIR spectrum of 1.32c ... 308 Figure F-3: UV/vis/NIR spectrum of 1.32g ... 308 Figure F-4: UV/vis/NIR spectrum of 3.3a ... 309 Figure F-5: UV/vis/NIR spectrum of 3.3c ... 309 Figure F-6: UV/vis/NIR spectrum s of 3.3f ... 310 Figure F-7: UV/vis/NIR spectrum of 3.5a ... 310 Figure F-8: UV/vis/NIR spectrum of 3.5c ... 311 Figure F-9: UV/vis/NIR spectrum of 3.5d ... 311 Figure F-10: UV/vis/NIR spectrum of 3.5f ... 312 Figure F-11: UV/vis/NIR spectrum of 3.6f ... 312 Figure F-12: UV/vis/NIR spectrum of 4.2c ... 313 Figure F-13: UV/vis/NIR spectrum of 4.2c (* spectrometer artifacts) ... 313 Figure F-14: UV/vis/NIR spectrum of 5.2b-trans ... 314 Figure F-15: UV/vis/NIR spectrum of 5.2b-cis ... 314 Figure F-16: UV//vis/NIR spectrum of 5.2h-trans (blue), [5.2h-trans]+ (red) and that obtained from the reduction of [5.2h-trans]+ (green) ... 315

Figure F-17: UV/vis/NIR spectrum of 5.2h-trans (blue), [5.2h-trans]- (red) and that obtained from the oxidation of [5.2h-trans]+ (green) ... 315

Figure F-18: UV/vis/NIR spectrum of 5.2h-cis (blue), [5.2h-cis]+ (red) and that obtained from the

reduction of [5.2h-cis]+ (green) ... 316

Figure F-19: UV/vis/NIR spectrum of 5.2h-cis (blue), [5.2h-cis]- (red) and that obtained from the

oxidation of [5.2h-cis]- (green) ... 316

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List of Numbered Compound

1.1 1.2 1.3

1.4 1.5

1.6 1.7 1.8 1.9

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xxiv 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19

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xxv 1.20a 1.20b 1.21 1.22 1.23 1.24 1.25 1.26 1.27

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xxvi

1.28

1.29 1.30 1.31

1.32

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xxvii

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xxviii

2.3

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xxix

3.4

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xxx

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-xxxi

5.1’ 5.1”

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xxxii [5.2h-trans]+ [5.2h-trans]- 6.1 6.2 6.3 6.4

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xxxiii

List of Abbreviations

1D one-dimensional 2D two-dimensional 3D three-dimensional A absorbance

A.U or a.u absorbance units

Å angstroms acac acetylacetonoate Ar aromatic group Bipy 2,2’-bipyridyl BODIPY 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene nBu n-Butyl o_C _{degrees Celsius} C carbon atom ca. approximately CH2Cl2 dichloromethane cm centimeter cm-1 wavenumber Cp cyclopentadienyl CT charge-transfer

Cu(OAc)2.2H2O copper(II)acetate dihydrate

CV cyclic voltammetry

d doublet

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xxxiv

DABCO 1,4-diazabicyclo[2.2.2]octane

DCM dichloromethane

DIPEA N,N-diisopropylethylamine

δ parts per million (chemical shift, NMR)

Δ heat or difference or denotes chirality

DFT density functional theory

DMSO dimethylsulfoxide

DPPH 1,1-diphenl-2-picrylhydrazyl

D2O deuterium oxide

ε molar extinction coefficient

e- electron

EI electron impact

emu electromagnetic units

EPR electron paramagnetic resonance

eq equivalents

Et3N triethylamine

eV electron volt(s)

Ecell electrode potential

Eox oxidation potential

Ered reduction potential

Et ethyl

Fc ferrocene

Fc+ ferrocenium

FMO frontier molecular orbital(s)

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xxxv

G Gauss

GalOA galactose oxidase

GHz gigahertz

H2O water

hfac 1,1,1,5,5,5-hexafluoroacetylacetonoate

HRMS high resolution mass spectrometry

HOMO highest occupied molecular orbital

Hz hertz

i or i ipso

IET intramolecular electron transfer

IR infrared

IVCT inter-valence charge-transfer

J coupling constant (NMR)

K Kelvin

kcal kilocalorie

Kc comproporptionation constant

λ wavelength

λmax wavelength of maximam electronic absorption

Λ denotes chirality

LLCT ligand-to-ligand charge transfer

LMCT ligand-to-metal charge-transfer

LUMO lowest unoccupied molecular orbital

m multiplet (NMR)

M molarity

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xxxvi

MeCN acetonitrile

μ denotes bridging ligation

μA microamps

μg microgram

MB mono-BF2 Nindigo chelate

MeOH methanol mg milligram MHz megahertz min minute(s) MLCT metal-to-ligand charge-transfer mol mole

mol-1 per mole

mmol millimole

MS mass spectrometry

mV millivolt

MV mixed valence

m/z mass per unit charge

N nitrogen donor

NacNac diketimine

NaOH Sodium hydroxide

nBuOH n-butanol

NIR near infrared

nm nanometer (10-9 m)

NMR nuclear magnetic resonance

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xxxvii

Oxi oxidation

O or o ortho

p para

Ph phenyl

ppm parts per million

q quartet (NMR)

RAL redox-active ligands(s)

Red reduction

s singlet (NMR)

s- per second

SOMO singly occupied molecular orbital

t triplet (NMR) or time t tertiary T temperature TCNE tetracyanoethylene TCNQ tetracyanoquinodimethane THF tetrahydrofuran

TLC thin layer chromatography

UV ultraviolet

V volt

vis visible

vs. versus

VT valence tautomerizm

XPS X-ray photoelectron spectroscopy

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xxxviii

Acknowledgments

Firstly I would like to acknowledge the efforts of my supervisor Dr Robin Hicks for guidance, support and patience. He gave me the freedom to develop as a synthetic chemist and was instrumental in building my confidence in communicating chemistry to others. I would also like to thank the Hicks-Frank household for numerous splendid social events and loaning me Zelly to walk on occasion.

Thank you also to Hicks group members past and present for personal and professional support as well as sharing synthetic ideas. Many thanks to Dr Steve MacKinnon, Dr Tyler Trefz, Dr Kevin Anderson, Bart Nowak, Cooper Johnston, Corey Sanz, Gennevieve Boice, Emma Nichols-Allison. Also, a big thank you to Aman Bains, Mark Zsombor and Aiko Kurimoto. In addition I would like to acknowledge the various undergraduate students that contributed to this work; Kate Waldie, Bryan Robertson and Brenden Peters.

I would like to thank the many staff and faculty of the chemistry department that have all contributed to making my time at UVic both enjoyable and academically fruitful.

Finally I would like to thank my team mate Meg. You have taught me so many things and I am blessed to have you in my corner.

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Dedication

For you, Mum.

……. If you can meet with Triumph and Disaster And treat those two impostors just the same….. - R. Kipling

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1

Chapter 1: Introduction

1.1 Ligand design

The world of coordination chemistry is symbiotic in such a way that for any chemical action to occur effectively it requires the mutual participation of both metal centre and ligand set that surrounds it. For this reason the use of ligand design to control the properties of coordination complexes pervades chemistry. There are a variety of ligand attributes that can be manipulated in order to control the reactivity at the metal centre. The steric nature, hapticity, denticity and hemi-lability of the ligand can be tuned to govern the availability of free sites, whilst electron donating and withdrawing groups can be selectively positioned to alter the electronic properties of the coordination complex. Amongst the first to achieve great success in tuning both the electronic and steric properties of coordination compounds were the cyclopentadienyl (1.1), polydentate phosphines (1.2) and polydentate amines and pyridines

(1.3).

1.1 1.2 1.3

Varieties of the above ligand groups can be seen throughout many aspects of inorganic and organometallic chemistry where they facilitate catalytic reactions at metal centres as well as numerous organic transformations.

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2

1.1.1 N-Donor ancillary ligands

One of the more recent successful examples of ligand design was the emergence of the ancillary ligand, β-diketiminate, commonly known as NacNac (1.4).1,2 This chelating ligand is the N-analogue of the acetylacetonate, acac, (1.5) ligand set. The conversion of the carbonyl moieties to imines introduces a point for tuning and controlling the properties of resulting complexes. As a result, a diverse range of coordination compounds incorporating NacNac have been explored.

1.4 1.5

Other π-conjugated polydentate ancillary ligands that are based on the isolobal replacement of O by NR include, but are not limited to, aminotoponiminates3 (1.6), diimino pyridines4,5 (1.7), α-dimines6,7 (1.8) and amidinates8,9 (1.9). The attractiveness of these ligand families stems from straightforward syntheses and the ability to tune the N-substituent.

1.6 1.7 1.8 1.9

1.2 Redox-active ligands (RALs)

Although ligands undoubtedly facilitate the chemistry of coordination compounds, in general they are spectators with respect to any chemical transformations. Owing to the redox potentials of the metal centre being more accessible than that of the surrounding ligand set, the electron transfer role is

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3 traditionally filled by the metal. A lot of chemical transformations involve two-electron chemistry, this requires metal centres that are able to change oxidation state by two. This attribute is generally reserved for precious metals (iridium, ruthenium, rhodium, osmium et al) and is why they can often be found at the heart of numerous catalysts. However, if the potentials of the ligand set and the metal centre can come close in energy, there is the possibility that the ligand can participate in redox changes itself. Ligand sets that are able to give and receive electrons, known as redox-active ligands (RALs), are now being investigated for their potential use in coordination compounds of earth abundant metals to perform catalytic and stoichiometric reactions.

Understanding the nature of the oxidation states of atoms, especially metal centres, is central to understanding the chemistry of molecules. The oxidation state concept, as illustrated by numerous textbooks, is frequently used and generally accepted to generate formal oxidation states. However, the concept is often disputed when it comes to physical (spectrochemical) oxidation states.10,11 In the mid 1960’s Christian Klixbüll Jørgenson described ligands as suspect (later non-innocent) after establishing non-integer oxidation state values for a series of complexes.11,12 Early pioneers in RAL chemistry suffered from the lack of analytical tools available to the modern chemist and as a result there was much debate over the assignment of oxidation states. One of the complexes at the centre of the early debates was a nickel (II) bisiminoquinone species. Two electronic structures were proposed, one a diradical (1.10) and the other involving the combination of a neutral and dianionic ligand set (1.11).13-15

1.10 1.11

As characterization methods become more advanced a clearer picture of the oxidation states of redox-active systems developed. The methods involved in elucidating the nature of redox events (spectroscopic, structural, magnetic and theoretical modeling)16 have been deemed so elegant that their use has been branded “art” by those involved.17 RALs mimic the abilities of transition metals in two important ways. They adopt more than one oxidation state and support an open-shelled configuration

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4 in one or more of these accessible oxidation states. One of the early RAL groups and still one of the most studied are the o-quinones18 (1.12), their nitrogen19 (1.13) and their mixed donor analogues20 (1.14).

1.12 1.13 1.14

It is the ability of these ligand sets to exist in a variety of oxidation states that resulted in a menagerie of complexes being synthesized and the conventional oxidation state assignment protocols being challenged (Figure 1.1).

Figure 1.1: The three oxidation states of o-benzoquinone type molecules (neutral quinone, monoanionic

semiquinonate, and the dianionic catecholate)

RALs have also been found to exist in several domains of bioinorganic chemistry with perhaps the best understood example being galactose oxidase (Figure 1.2). The two-electron redox chemistry required for the oxidation of an alcohol to an aldehyde arises from the cooperation of both the copper centre and the coordinated phenoxyl ligand.11,21

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5

Figure 1.2: The active site of galactose oxidase (GalOA)

Several synthetic mimics for GalOA have been developed incorporating a variety of RALs.22 Two examples are shown below involving ortho-iminosemiquinonate23 (1.15) and Salen type ligands24 (1.16).

1.15 1.16

More recently, complexes containing RALs have been shown to facilitate catalytic and stoichiometric reactions including bond forming reactions, disproportionations, hydrosilylations, and water and alcohol oxidations.25-31 The RAL acts as a reservoir that stores/shuttles electrons to and from the active site when needed. In some cases the RAL is the sole supplier of electrons with the metal centre acting as a static anchor where the substrates can come together (Figure 1.3).32,33

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6

Figure 1.3: Ligand based redox chemistry facilitating ‘molecular reductive elimination’ (top) and

cycloaddition (bottom) reactions

1.2.1 Redox-active bridging ligands

Whilst RALs that bind to a single metal centre have become somewhat prevalent, RALs that are able to bridge between more than one metal are less common. Of the somewhat sparse examples in the literature, those based on the benzoquinoid family of molecules are again the most common (1.17.34-36 Despite the popularity of phosphorous containing moieties in ancillary ligation, examples of coordination compounds involving phosphorous based redox-active bridging ligands are limited to just one family, bis(phosphinyl)hydroquinone (1.18), with the use of this ligand in bimetallic complexes limited to just three examples.37,38 Polymeric bis(pyrazole)quinone (1.19) chains involving copper centres have also been studied, in this case for their 1D magnetic properties.39 The redox-activity of all three ligand sets arises from the readily accessible catecholate, semiquinonate and quinone redox states.

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7 Another example of a conjugated redox-active bridging ligand system is the polynitriles. Ligands based on tetracyanoethylene (1.20a) and tetracyanoquinonedimethane (1.20b) have been shown to exhibit redox-active behavior as well as a variety of 1D, 2D and 3D networks that display interesting conducting properties.40,41 Related to 1.20 are systems based on N,N’-dicyanobenzoquinonedimines (1.21). Selected complexes of 1.21 exhibit high conductivities with significant tolerance of functionality allowing for high levels of control.42 The redox-activity in these systems arises from the numerous cyano groups present in conjugation. This gives rise to low energy π* orbitals and renders the ligand sets highly electron accepting and thus stable radical anions and dianions are accessible.

1.20a 1.20b 1.21

Tetrazines (1.22) have also been shown to effectively bridge metals and, depending on the nature of the 3,6-substituents (X), the degree of nucleation can be controlled.43 2,2’-azobypyridine (1.23) and related ‘S-frame’ azo containing functions have also been probed as redox-active bridging ligands.44 Both 1.22 and 1.23 are strongly electron accepting and can be reduced to give radical anionic and dianionic ligand redox states.

1.22 1.23

Finally, bipyrimidines (1.24) and multidentate pyrazine derivatives (1.25) have been shown to effectively bridge metal centres. These ligand sets are able to undergo reversible one-electron reductions to generate radical anions.

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8

1.24 1.25

All of the above examples (and RALs in general) possess extended π-delocalization. This aids in both accessing and stabilizing various redox states. However, in most cases these ligands lack the potential for derivitization and so cannot be easily tuned. Examples of tunable multidentate bridging RAL systems are rare. One such example is bis(imino)acenapthene (TIP) (1.27).45,46 This is the bifunctional analogue of the redox-active capping ligand, BIAN (1.26). Control of the resulting coordination compounds properties can be gained by varying the N-substituents. 1.27 can undergo two reversible one-electron reductions at both imine functionalities with the resulting dianion exhibiting significant delocalization over both diazabutadiene moieties.

1.26 1.27

1.3 Indigo

One of the earliest known dyes, the use of indigo (1.28)47 dates back millennia where it was used all over the globe for its intense colour.48 Indigo was originally extracted indirectly from the leaves of plants belonging to the genus indigofera. Owing to the difficulty in obtaining indigo in any substantial

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9 quantities and the difficulties with manipulating it to dye fabrics, it was such a luxury that it was often referred to as blue gold.

1.28

Despite its wealth of history, the structure of indigo was not established until 1883 by Nobel laureate Adolf Von Baeyer.49 (Its trans configuration was not determined until 1928)50. The structural elucidation resulted in a boom of synthetic procedures to produce indigo on a commercial scale. Some 38,000 tonnes of indigo are now produced per annum with the primary use being to dye denim.51,52

Compared to similar sized conjugated molecules, indigo exhibits unusually long wavelength absorption. A variety of calculations on indigo have established that the chromophore consists of two donor groups (NH) and two acceptor group (C=O) in a doubly cross conjugated arrangement (Figure

1.4).53-57 The donor groups raise the energy of the HOMO and acceptor groups lower the energy of the LUMO resulting in the low energy transition.57,58

Figure 1.4: The fundamental “H-chromophore” of Indigo

In general indigo is seen as blue in colour. However, it exhibits different colours depending on its phase and solid state morphology (gas phase λmax = 540 nm, crystalline λmax = 675 nm, amorphous λmax = 650 nm)59,60. In addition, the planarity of the molecule gives rise to aggregation effects in solution that

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10 alters the colour of the dye under certain conditions. At high concentrations or low temperatures indigo undergoes J-type aggregation resulting in a red shift of λmax from 603 nm to 700 nm (Figure 1.5).61

Figure 1.5: UV/vis/NIR spectra of indigo at varying concentrations (left) and varying temperature (right)

(reprinted with permission from Molecules)61 along with a photo of a saturated solution of indigo in DCM

In solution, indigo exhibits positive solvatochromism resulting in colour variance from violet to blue. This is as a result of the ground state being neutral with the excited state being a combination of charge separated resonance structures (Figure 1.6).59

Figure 1.6: Resonance contributions to the indigo excited state

Other highly coloured indigo derivatives exist that possess various functional groups on the peripheral rings. Tyrian purple (1.29) contains bromines on the benzannulated rings and the water soluble indigo carmine (1.30) possesses sulfonate groups. These additional subsituents somewhat perturb the electronic spectra resulting in the compounds displaying different colours. Derivatives with different donor units also exist resulting in dramatic colour changes. Thioindigo (1.31) contains two

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11 sulfur atoms in place of the NH groups and is deep red in colour. The inherent problem with all simple indigo derivatives is their extreme lack of solubility. Whilst this may be desirable for their pigment based applications, this insolubility is a hindrance for performing coordination chemistry.

1.29 1.30 1.31

In order to address the solubility issue, numerous bulkier indigoid compounds have been synthesized (Figure 1.7). Whilst various new derivatives have been shown to have improved solubility, their syntheses are not straightforward and require multi step reactions. 62-64

Figure 1.7: Bulkier indigoid derivatives

1.3.1 Coordination chemistry of indigo

Despite possessing some inherently attractive features structurally - with a bis-bidentate chelating motif - and economically - with its relative inexpense and commercial availability, the use of indigo, and closely related molecules, in coordination chemistry has been limited to just a handful of examples. In the early 20th century a variety indigo chelate complexes of copper, nickel, zinc and cobalt were reported, but owing to a lack of characterization techniques their structures were left somewhat in

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12 doubt.65-70 It was not until the latter part of the century that palladium and platinum complexes of indigo were conclusively synthesized (Figure 1.8).71-72 Whilst these compounds were fully characterized, their capacity to undergo chemistry was not investigated. This was likely because they maintain the same high degree of insolubility as their parent indigoids. This issue was addressed by employing saturated indigo derivatives e.g. octahydroindigo. The fundamental chromophore is preserved but the resulting complexes possess slightly more freedom and thus do not adopt a planar geometry.73

Figure 1.8: Early indigo based coordination complexes, Indigo[Pd(nBuP)3Cl] (left) and octahydroindigo[Pd(Cl)PEt3]2 (right)

The coordination chemistry of indigo remained largely undeveloped until its incorporation into an elaborate hexarhenium cluster reported in 2008.74 This exotic molecule was later shown to possess rich redox behaviour and NIR absorption , both of which are ligand centered in origin (Figure 1.9).75

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1.3.2 Previous Nindigo research

The inherent insolubility and lack of facile routes to derivitization renders indigo challenging to exploit as a bridging ligand. Much in the same way as NacNac was developed as an extension to acac, one could envision the same conversion of indigo to the N-analogue (Nindigo), 1.32. The resulting molecule seemed to be a potentially attractive bridging ligand where the N-subsituents could improve solubility as well as offer a handle for tuning the attributes of resulting coordination compounds.

1.32

The first reported synthesis of indigo diimines was in 1909.76 The simplest of all previous syntheses, indigo was heated in neat aniline in the presence of boric acid, the latter perhaps acting as both a drying and activating agent to promote the forward condensation reaction. However, this synthesis has since been brought into disrepute due to problems with reproducing the data.77 Alternative pathways have involved the thermal oligomerisation of aryl isocyanides78 and reactions of bis-imidoylchlorides of oxalic acid with powdered magnesium (reducing agent) under ultrasonic conditions.77,79 The poor yields combined with complex syntheses and limited substrate scope renders these methodologies of limited use in ligand design.

Unactivated ketones have been reported to be activated by TiCl4 during the formation of N-sulfonylimines (Scheme 1.1).80 The TiCl4 was thought to act as both a Lewis acid activator and drying agent with an auxiliary base employed to mop up the generated HCl. The use of TiCl4 was subsequently shown to aid the conversion of the carbonyl groups of anthraquinone to imines (Scheme 1.2).

Synthesis, Redox and Spectroscopic Properties of Nindigo and a Variety of Nindigo Coordination Compounds

Synthesis, Redox and Spectroscopic Properties of Nindigo and a Variety of

Nindigo Coordination Compounds

Supervisory Committee

Synthesis, Redox and Spectroscopic Properties of Nindigo and a Variety of

Nindigo Coordination Compounds

Abstract

Table of Contents

List of Tables

List of Schemes

List of Figures

List of Numbered Compound

List of Abbreviations

Acknowledgments

Dedication

Chapter 1: Introduction

1.1 Ligand design

1.2 Redox-active ligands (RALs)

1.3 Indigo